An acrylic rubber is a rubber material which is excellent in heat resistance, oil resistance, weather resistance and the like. An acrylic rubber is therefore widely used for automotive rubber components such as gaskets, hoses, O-rings, seals. These days, the requirements for the properties of rubber components such as heat resistance, oil resistance and long lasting property have been increased due to higher-grade automobiles or automobiles having improved performance, and a crosslinkable blend material of a fluororubber and an acrylic rubber which is further excellent in heat resistance, oil resistance, long lasting property and the like has been developed.
However, in a crosslinkable blend material where both or either of the two rubber components of an acrylic rubber and a fluororubber are crosslinked, it is difficult to stably disperse the both rubber components of the acrylic rubber and the fluororubber for a long time. This causes a problem that the properties such as mechanical strength are degraded over time. In order to solve this problem, the applicant of the instant application proposes a vulcanizable acrylic rubber-fluororubber composition comprising: (A) a rubber component comprising a mixture of an acrylic rubber comprising 1 to 20 mol % of a crosslinkable group-containing polymer unit having crosslinkable hydroxyl groups or crosslinkable chlorine atoms, and a fluororubber which is a propylene hexafluoride homopolymer or a copolymer of propylene hexafluoride and vinylidene fluoride and/or ethylene tetrafluoride, wherein the weight ratio of the acrylic rubber to the fluororubber is 0.5 to 99.5/99.5 to 0.5; (B) an acid acceptor comprising a metal oxide and/or a metal hydroxide; and (C) a vulcanization accelerator comprising quaternary ammonium salt and/or quaternary phosphonium salt and not comprising a vulcanizing agent (see Patent Document 1).
When a vulcanizable acrylic rubber-fluororubber composition is used for automotive rubber components and the like, it is desired that compression set resistance is further improved.